The Cameron SIF System: Combining SIF measurements with High-Resolution Imagery for Complex Canopy Characterization

Abstract:

Recent measurements of Solar Induced Fluorescence (SIF) from spectrometers on satellites have been used to quantify ecosystem productivity on global and regional scales. Instruments installed on towers have also accurately measured SIF in forest canopies and crops. However, measuring SIF from complex targets such as trees in urban landscapes presents unique challenges. We present a new instrument (Cameron) that combines narrow field-of-view spectrometers measuring SIF and photochemical reflectance index (PRI) with a co-aligned high-resolution camera. This allows for the accurate remote measurement of SIF and PRI simultaneously from individual trees, and even different portions of the crown on a single tree, even at distances of hundreds of meters. The addition of camera imagery allows us to leverage advanced image and video processing techniques to characterize other factors that affect SIF measurements, such as shade, fill-factor, leaf angle, and wind. The Cameron system is autonomous, self-aligning, and weatherproof, making it ideal for both short- and long-term installations. Several Cameron systems were built, tested, and deployed in the summer of 2020. Initial measurements taken in both urban and sub-urban locations show large variations in the magnitude of SIF measured across different trees, over the course of a day, and throughout the growing season. These observations provide important insight into both productivity of complex ecosystems and what environmental and technical factors affect our ability to accurately measure SIF and understand light energy partitioning more completely to improve estimates of ecosystem productivity. Understanding how SIF retrievals vary at this scale is critical to bridge the gap between satellite observations and leaf-level processes.